The present invention relates to a linear access mechanism which is used as positioning means in a magnetic disk apparatus, and more particularly to a linear access mechanism which is required to have a high positioning accuracy.
In a conventional magnetic disk apparatus having a linear access mechanism, a reaction force which is applied to the linear access mechanism as the reaction of a driving force is absorbed by the rigidity of the whole of the magnetic disk apparatus, or the linear access mechanism is provided with a reaction absorbing mechanism used in guns. The reaction absorbing mechanism utilizes the damping effect due to friction as described in a Japanese utility model application Laid-open No. 49-49,799, absorbs reaction by vibrating a striking piston and a reaction piston simultaneously so that a phase difference of 180.degree. is generated therebetween as described in a Japanese Patent Application laid-open No. JP-A-58-132,470, or utilizes a reaction force due to the jet of a high pressure gas as described in a Japanese utility model Publication No. 49-9,680.
The linear access mechanism of a magnetic disk apparatus is driven at a mean frequency of 20 to 30 Hz in a seeking operation, and is driven at a frequency which is ten or more times higher than the above mean frequency in a following operation. In a case where the reaction force applied to the linear access mechanism is absorbed by the rigidity of the magnetic disk apparatus, the absorbing operation cannot follow such a wide frequency range. Moreover, abrasion is generated in a friction surface, and thus the reliability of the magnetic disk apparatus is degraded. Further, in a case where the reaction absorbing mechanism is used, the reaction absorbing mechanism cannot follow vibrations in such a wide frequency range, and moreover is readily affected by temperature.